Elizabeth Vargas Balances Work & Motherhood

Elizabeth Vargas didn't get much rest during her maternity leave: Since giving birth August 16, she's been caring for newborn Samuel Wyatt, while trying to keep son Zachary, 3, happy as well.

"That mantra 'sleep when the baby sleeps', doesn't work when you have a three year old," Vargas, 44, tells PEOPLE. "I'm still struggling to find enough time to give Zachary all the TLC he deserves when I'm up around the clock nursing the baby."

Although Vargas says her son has struggled with the new addition to the family, "he talks all the time about the things he's going to teach him – how to ride a bike and build blocks," she says. "My husband (Grammy-winning singer Marc Cohn, 47) and I have to continually remind Zachary that it takes a long time for a baby to be able to do anything fun. They're kind of blob like for awhile."

And that blob needs constant attention. "Samuel has a very sensitive tummy and a little bit of colic," says Vargas. "I know they outgrow it, but there's nothing more heartbreaking than watching your newborn cry and scream in pain."

One of the biggest hurdles though is lack of sleep – as most new parents know. "I haven't slept more than 90 minutes at a time in a month – I'm practically hallucinating," says Vargas.

Still in terms of her body, she says she's feeling better and anxious to fit into her old pre-baby clothes. "Even though (my) body still isn't back to normal – and shouldn't be if you're nursing, to be honest – I feel much more like myself. I'm looking forward to being able to squeeze back into all my old clothes at some point."

Vargas took 10 weeks leave from her job at ABC, but that's not to say she hasn't been working. "I am on the phone several times a week planning and booking stories and I start shooting some interviews in October. My first night back we have a major project airing."

The topic is something Vargas knows a thing or two about. "We have decided to address the issue of whether or not working mothers can have it all," she says. "Obviously, I'm exhibit A for: you can't. At least, not if "all" is defined as anchoring World News Tonight."

Indeed, Vargas has become an unwitting poster-woman for working moms. Though she scored the job of ABC co-anchor opposite Bob Woodruff just last August, Vargas discovered she was pregnant this February, one month after Woodruff was seriously injured on assignment in Iraq. With the anchor lineup forced to change, ABC offered Vargas the chance to anchor 20/20, and handed the World News job to Charles Gibson.

"Anchoring World News Tonight is a tremendously demanding job and there is a very little flexibility," says Vargas. "In order to do that job, you're talking 13-15 hours days, five days a week, sometimes seven days."

Though she worked on that schedule for a year and a half, Vargas didn't want try that routine with a newborn. "Zachary paid a price for that. He struggled with my absence," she says of her toddler. "When your child cries because you have to leave or you're not home, it's hard to ask him to understand that mommy's career is more important."

Despite the step back, Vargas insists she isn't stepping down. "Samuel and Zachary will get older and I fully intend to work as hard as I can to get another opportunity to anchor a daily broadcast," she says. "I hope I get that chance. I think I proved myself – I just couldn't do it now."